Field of the Invention The present invention relates to a land based aquaculture tank for the culture of aquatic animals such as crustaceans, fish and molluscs and in particular, but not exclusively, a tank for the culture of lobster phyllosoma.

Background of the Invention

Global wild stocks of many aquatic animals, including tropical rock lobster and slipper lobster, are compromised due to changing environmental conditions and weather patterns, overfishing and poor fisheries management. As a

consequence, most wild fisheries are in decline and there is a growing trend to propagate aquatic animals in land-based aquaculture tanks. Throughout this specification the term "aquatic animals" is intended to mean an animal which lives in the water for all or most of its life in water whether the water is freshwater or salt water. Due to the fragile and delicate nature of aquatic animals particularly in the early stages of their life cycle, farming aquatic animals in land-based tanks on a commercially viable scale is particularly difficult. Tight control is often required in relation to water quality, water temperature, oxygenation, water flow within an aquaculture tank and density of animals contained in volume .of water. While there is a variation in the robustness of aquatic animals it is known, for example, that some crustaceans are particularly delicate as they moult multiple times during their larval cycle. At these times mechanical damage from the larvae coming into contact with side walls of a tank, or equipment within a tank such as filters, is often fatal.

Summary of the Invention

In one aspect the invention provides an aquaculture tank comprising:

a receptacle capable of holding a volume of water and a plurality of aquatic animals; and,

an inlet system through which water flows into the receptacle, the inlet system capable of directing water to flow into the tank in an upward direction along a central axis from a bottom of the receptacle, and tangentially to an inside surface of the receptacle to generate a flow of water that circulates about the central axis. The inlet system may comprise a first inlet structure which facilitates the upward flow of water, the first inlet structure comprising a first inlet located at the bottom of the receptacle.

The first inlet structure may comprise an expansion chamber upstream of the first inlet.

The first inlet structure may comprise an inlet pipe upstream of the expansion chamber, wherein the expansion chamber has a maximum internal diameter greater than an internal diameter of the inlet pipe.

The maximum internal diameter of the expansion chamber may also be greater than a maximum internal diameter of a first inlet.

The first inlet, expansion chamber and inlet pipe may be co-axial with the central axis.

The inlet system may further comprise a second inlet structure which facilitates the circulating flow, the second inlet structure comprising at least one second inlet formed in a side wall of the receptacle the or each second inlet configured to deliver water into the tank with a direction of flow substantially tangential to an inside surface of the receptacle adjacent the second inlet.

The second inlet structure may further comprise respective second inlet pipe coupled with respective second inlets. The second pipes may be inclined wherein an end of the second inlet pipe adjacent a respective second inlet is vertically lower than an opposite end of the second inlet pipe.

The first and second inlet pipes may be in fluid communication with each other. The tank may comprise respective valves operable to vary a proportion of water flowing to the first inlet and the second inlet. The tank may also comprise an air injection system capable of injecting air into the upward flow of water.

The tank receptacle may have an inner surface that is smoothly curved about the central axis.

The receptacle may comprise a frusto-conical portion having a small diameter end and a large diameter end, wherein the bottom of the tank is at the small diameter end of the frusto-conical portion, and the upward flow of water flows through the small diameter end.

The receptacle may comprise a constant diameter portion formed contiguously with the large diameter end of the frusto-conical portion, and wherein water generating the tangential flow enters the receptacle through the constant diameter portion.

The receptacle may have an upper edge which water overflows to exit the receptacle; and, an outlet system capable of handling water overflowing the upper edge, the outlet system comprising a screen having openings sized to block passage of aquatic animals held in the receptacle, and a gutter system which collects the water overflowing the upper edge from about an entire periphery of the receptacle and drains the overflowing water.

The gutter system may comprise a first gutter extending about the upper edge on an outside of the receptacle and a second gutter extending about the first gutter with a dividing wall between the first and second gutters, wherein water in the first gutter which overflows the dividing wall flows into the second gutter; the second gutter having at least one outlet through which water in the second gutter is drained.

The dividing wall may be adjustable in height to facilitate adjustment of depth of the first gutter.

The dividing wall may comprise a first fixed portion and a second adjustable portion coupled to the first fixed portion to facilitate axial motion of the second adjustable portion relative to the first fixed portion. The dividing wall may be provided with one or more screened holes near a lower end of the dividing wall through which water flows from the first gutter to the second gutter. The second gutter may be provided with at least two outlets.

The at least two outlets are evenly spaced about the second gutter.

In one embodiment of the tank the upper edge of the receptacle is tapered to reduce in thickness, the taper configured to direct water on the upper edge to flow toward the receptacle.

However in an alternate embodiment the upper edge is formed with a circumferential shoulder on an inside surface configured to seat the screen.

In a second aspect the invention provides an aquaculture tank comprising: a receptacle capable of holding a volume of water and a plurality of aquatic animals, the receptacle having a side wall with an upper edge;

an inlet system through which water flows into the receptacle; and, an outlet system capable of handling water overflowing the upper edge, the outlet system comprising a screen having openings sized to block passage of aquatic animals from the receptacle into the outlet system, and a gutter system capable of collecting water overflowing the upper edge from about an entire periphery of the receptacle and subsequently draining the overflowing water.

The gutter system, the inlet system and the outlet system in the second aspect may be the same as in the first aspect. In a third aspect the invention provides a method of rearing aquatic animals comprising:

providing a tank capable of holding a volume of water and a plurality of aquatic animals;

placing a volume of water and plurality of aquatic animals in the tank; and,

generating first and second flows of water within the tank, the first flow comprising an up flow of water from a central location at the bottom on the tank to a top of the tank;

and the second flow. comprising a circulating flow of water which circulates about the up flow of water. The first flow comprises an outward flow from the up flow at the top of the tank toward an upper edge of the tank, and a down flow back to the central location at the bottom of the tank to thereby generate a toroidal-like flow of water upwardly through the centre of the tank and downwardly near an inside surface of the tank.

The method may comprise overflowing a portion of the water through a screen disposed about the upper edge of the tank, and forming the screen with opening which prevents passage of aquatic animals therethrough. The method may comprise providing a first gutter about the upper edge into which the overflowing portion of water flows.

The method may comprise overflowing water in the first gutter into a second gutter provided adjacent the first gutter.

The method may comprise providing a dividing wall of adjustable height between the first and second gutters and over which water in the first gutter flows to reach the second gutter, wherein depth of the first gutter is adjustable by adjusting the height of the dividing wall.

The method may comprise injecting air into the up flow of water from a location at or near the bottom on the tank.

Brief Description of the Drawings

An embodiment of the present invention will now be described by way of example only with reference to the accompanying drawings in which:

Figure 1 is a schematic representation of an aquaculture tank in accordance with an embodiment of the present invention;

Figure 2 is a plan view of the aquaculture tank shown in Figure 1 ; Figure 3 is a section view of an upper portion of the tank and illustrating an outlet system incorporated in the tank; Figure 4 is a schematic representation of an expansion chamber incorporated in an embodiment of the aquaculture tank; and,

Figure 5 is a schematic representation of a receptacle incorporated in a second embodiment of the aquaculture tank.

Detailed Description of Preferred Embodiment

An embodiment of an aquaculture tank is arranged to generate multiple flows of water in different directions. One flow is an upward flow of a column of water from a central location at a bottom of a tank. When the water in this column reaches a top of the tank flows it laterally toward an upper peripheral edge of the tank. A portion of this water overflows the edge and is collected in an outlet system while the remaining portion of the water flows back down along an inside surface of the tank to a location where it again joins the up flow. This generates an upwelling, toroidal-like flow of water within the tank. A further flow of water is generated which circulates about the upward flowing column of water which coincides with a central vertical axis of the tank. The toroidal-like flow of water spreads feed for the aquatic animals throughout the tank. The circulating flow generates a force on the aquatic animals which tends to keep them away from the tank wall and thus avoid collision or impact with the inside surface.

A further aspect of an embodiment of the aquaculture tank is an outlet system which handles water that overflows the upper edge of the tank. A screen extends about the upper edge to prevent the passage of aquatic animals from the tank to the outlet system. The outlet system is configured to enable water to overflow evenly about the entire upper edge of the tank; generating an even flow rate of water over the upper edge and across the entire circumference of the screen. An adjustable wall in the outlet system enables variation in the total area of the screen through which water overflows into the outlet system.

Figure 1 illustrates an embodiment of an aquaculture tank 10. The tank 10 comprises a receptacle 12 capable of holding a volume of water and a plurality of aquatic animals, such as but not limited to lobster larvae or phyllosoma. The tank has an inlet system 14 through which water flows into the receptacle 12. As described in greater detail below, the inlet system 14 is capable of directing water to flow into the tank in an upward direction along a central axis 16 from a bottom 18 of the receptacle 12. This generates an upward flowing column of water 100. The inlet system 14 also directs water to flow tangentially to an inside surface 20 of the receptacle 12 to generate a flow of water that circulates about the central axis 16 and the upward flowing column of water.

The tank 10 also comprises an outlet system 22 that handles the water overflowing an upper edge 24 of the receptacle 12. The outlet system 22 extends wholly about the upper edge 24 so that water can flow evenly out of the receptacle 12 over the upper edge 24. This generates a uniform flow rate of water out of the receptacle 12. Water flowing into the outlet system 22 is subsequently drained through one or more outlets 26. The outlet system 22 also includes a screen 28 which extends about the edge 24. The screen 28 is provided with openings of a size to prevent the passage of aquatic animals from the receptacle 12 into the outlet system 22.

Looking at the features of the tank 0 in more detail, the receptacle 12 comprises a frusto-conical portion 30 having a small diameter end which coincides with the bottom 18 of the receptacle and a large diameter end 32 which is downstream of the bottom 18 with reference to the up flow of water along the axis 16. The receptacle 2 also comprises a constant diameter portion 34 formed contiguously with the large diameter end 32 of a frusto- conical portion 30. This structure results in the inside surface 20 of receptacle 12 being smoothly curved. The inlet system 14 comprises a first inlet structure 36 and a second inlet structure 38 which are in fluid communication with each other via a conduit 40.

The first inlet structure 36 comprises a first inlet 42 located at the bottom 18 of the receptacle 12, an expansion chamber 44 upstream of the first inlet 42, and an inlet pipe 46 upstream of the expansion chamber 44. The inlet 42, expansion chamber 44 and inlet pipe 46 are co-axial with each other and with the central axis 16. The expansion chamber 44 has a maximum inner diameter which is greater than the diameter of the inlet 42 and of the inlet pipe 46. The inner diameter of the expansion chamber 44 decreases in opposite directions from the maximum diameter so that opposite ends of the expansion chamber 44 have diameters coincidental with the diameters of the inlet 42 at one end, and the inlet pipe 46 at an opposite end. The purpose of the expansion chamber 44 is to equalize water velocity and pressure of the inflowing water and assist in directing the up flowing water to flow evenly as a column along the central axis 16. A lower end of the inlet pipe 46 is provided with a valve 48 to allow for drainage and waste extraction from the tank 10.

As shown in Figure 4 expansion chamber 44 is provided with an internal baffle block 45 about which water entering the tank 10 from inlet pipe 46 must flow about and around in order to reach the inlet 42. Baffle block 45 has a planar bottom surface 47 lying in a horizontal plane and thus generally perpendicular to the direction of flow of water from the inlet pipe 46. Bottom surface 47 spans an area approximately the same as, and is located to substantially underlie, the inlet 42. The baffle block 45 tapers to an apex 49 in the downstream direction referenced to the direction of inflowing water to the tank 10 from the inlet pipe 46. In alternate embodiments baffle block 45 may comprise: a generally conical shape and thus a continuously curved side wall 51 ; or, a pyramidal shape, in which case the side wall 51 is composed of a number of planer surfaces. In each embodiment however side wall 51 of the baffle block is sloping or inclined. This assists in the dispersion of waste material when valve 48 is opened to drain and remove waste from the tank 10. Waste in the tank 10 strikes the side wall 51 and is thus dispersed about the baffle block 45 and entrained in the out flowing water. This reduces the possibility of a conglomeration or wad of waste material blocking the valve 48. In contrast if a planar surface were presented to the out flowing water when extracting waste, the waste would simply sit on the surface in the inlet and would re-suspend once water was returned to the tank 10, thus reducing water quality.

With particular reference to Figures 1 and 2, the second inlet structure 38 comprises a second inlet 50 formed in the receptacle 12 and more particularly in the constant diameter portion 34, and a second inlet pipe 52 that leads to and is in fluid communication with the second inlet 50. The second inlet 50 and the second inlet pipe 52 lie along a common line substantially tangential to inside surface 20 of receptacle 12 adjacent the inlet 50. In one embodiment this line may be inclined to the horizontal so that the inlet 50 is at a lower height than an end of the inlet pipe 52 distant the receptacle 12. This gives the water entering the tank 10 a combined sideways and downward trajectory. The water entering tank 10 from the second inlet structure 38 generates a circulating flow of water about the central axis 16 and upward flowing water column 100.

The inlet structure 14 also comprises a main inlet structure 54 which supplies water to both the first inlet 42 and the second inlet 50. The main inlet structure 54 comprises a valve 56, a one-way valve 58 and a conduit 60 which is in fluid communication with both the first inlet .42 and the second inlet 50. A flow meter 62 is disposed in conduit 60. A T-coupling 64 provides fluid communication between the conduit 60 and both the conduit 40 and the conduit 52. Thus water from a supply (not shown) initially passes through the valve 56 and oneway valve 58, through the conduit 60 and flow meter 62 and is then split between the first inlet 42 and the second inlet 50. The proportion of water diverted to the respective inlets 42 and 50 is controlled by valves 66 and 68. The valve 66 is provided in the conduit 40 adjacent the first inlet pipe 46. The valve 68 is disposed in the second inlet pipe 52 intermediate the second inlet 50 and the T-coupling 64.

In the illustrated embodiment the second inlet structure 38 is depicted as having one second inlet 50. However in alternate embodiments the second inlet structure 38 may have more than one inlet. For example two second inlets 50 can be provided at diametrically opposite locations which direct water to flow in the same direction about the central axis 16. In such an embodiment a manifold provides fluid communication between the valve 68 and corresponding second inlet pipes 52 for each of the second inlets 50.

A screen 70 is provided across the first inlet 42 and a second screen 72 is provided between the second inlet 50 and the valve 68. The screens 70 and 72 are configured to prevent the passage of aquatic animals therethrough. The provision of the one-way valve 58 prevents any backflow of water through the inlet structure 14 in the event that there is a cut-off in supply of water to the valve 56.

The tank 10 is provided with an air injection system 74 which is capable of injecting air into the upward flowing water column 100 in the tank 10. The air injection system 74 comprises a manifold 76 located about the inlet 42 at the bottom 18 of the receptacle. Valves 78 are placed at each end of the manifold 76 to control the inflow of air from a blower or compressor (not shown). The manifold 76 is provided with a plurality of holes (not shown) located within the inlet 42 to allow air to bubble into the upward flow of water.

With particular reference to Figures 1 and 3 the outlet system 22 comprises the screen 28 and a gutter system 80 which collects water overflowing the upper edge 24 and passing through the screen 28, from about the entire periphery of the receptacle 12 and drains the overflowing water. The.overflowing water may be drained either to a filter (not shown) and recycled into the tank 10, or alternately it may be dumped. The screen 28 is attached to a ring 82 which fits snugly against an outside surface of the receptacle 12 adjacent the upper edge 24. The ring 82 fits sufficiently snugly to prevent the formation of any gaps through which aquatic animals or their feed can pass to flow into the gutter system 80 but can be decoupled to enable the replacement, if necessary, of the screen 28 for cleaning or changing with a screen with different mesh (aperture) size. The gutter system 80 comprises a first gutter 84 that extends about the upper edge 24 on an outside of the tank 10, and a second gutter 86 which extends wholly about the first gutter 84. The gutters 84 and 86 are separated by a dividing wall 88. The dividing wall 88 is adjustable in height to enable adjustment of the depth of the first gutter 84. The screen 28 is of a height greater than that of wall 88 to prevent animals escaping the receptacle 12. As previously described the outlet system 22 and in particular the arrangement of the first and second gutters 84 and 86 generates a even flow of water across the entire circumference of the screen 28. This is in contrast to a single gutter with one or more outlet apertures (drains) in which case there would be a significantly greater water velocity through portions of the screen near the outlet aperture(s).

The dividing wall 88 comprises a first fixed wall 90 ^' which extends upright from a bottom wall 92 of the gutter system 80 and a ring 94 which slidably and sealingly fits onto the wall 90. The fitting of the ring 94 on the wall 90 enables axial displacement of the ring 94 relative to the wall 90 to enable height adjustment of the dividing wall 88 while preventing any substantive flow of water between the wall 90 and ring 94 into the second gutter 86. Adjusting the height of the dividing wall 88 increases the surface area of the screen 28 through which water passes from the tank 10 into the outlet system 22 thereby reducing water velocity through the screen. Alternately the height of the dividing wall can be lowered to decrease the surface area of the screen 28 through which water passes thereby increasing water velocity through the screen 28.

In order for water to be drained from the outlet system 22, water which flows into the first gutter 84 must overflow the dividing wall 88 into the second gutter 86. The second gutter is provided with one or more outlets 26 through which water in the second gutter 86 is drained. The water level in the tank 12 is governed by the top of dividing wall 88, whilst the water level in the second (i.e. outer) gutter is lower as the water is being drained from the second gutter 86 at a rate faster than it is flowing in. The water travels over wall 88 evenly around the entire circumference / periphery of wall 88 and cascades into the outer gutter 86.

As shown most clearly in Figure 3, the upper edge 24 of the receptacle 12 is formed with a taper 96. The taper 96 is configured so that aquatic animals or food stuff on the taper 96 is directed by action of gravity to flow into the receptacle 12. The provision of the taper 96 thus assists in preventing the lodging of aquatic animals and food onto the upper edge 24.

Figure 5 shows an alternate embodiment of the tank 10' in which the same reference numbers as used hereinbefore in describing the tank 10 are applied to the same or like features. The tank 10' differs from the tank 10 only in the manner of coupling of the screen 28 to the receptacle. In this embodiment inside surface 20 of receptacle 12 adjacent the upper edge 24 is provided with a circumferential rebated shoulder 97 which is configured to seat the screen 28. The shoulder 97 is designed to be of a depth equal to the thickness of a lower end of the screen 28 so that when the screen is seated on shoulder 97, an inside surface 99 of the screen 28 is flush with inside surface 20. This obviates the need for the taper 96 of the tank 10. As shown in Figure 1 , the tank 10 is further provided with one or more sockets 98 near the upper edge 24. The sockets 98 enable coupling with other devices to facilitate various operations including, for example, transfer of aquatic animals from the tank 10 to another tank, or connection with waste extraction system or water quality analysis systems.

An example of the operation and function of the tank 10 will now be provided.

Assuming that the tank 10 is initially empty, the tank is filled with water by connecting a water supply hose to the valve 56, and opening valve 56, 66 and 68. This will enable water to be introduced into the tank 10 through the first inlet 42 and the second inlet 50. The proportion of water entering from the inlets 42 and 50 may be regulated by the valves 66 and 68. Once the tank 10 is filled, the flow of water into the tank can also be regulated by the valves 56, 66 and 68. Generally, water will continue to flow into the tank 10 with a portion of water flowing out of the tank 10 through the outlet system 22. Water overflowing upper edge 24 through screen 28 and flowing into the outlet system 22 may be either drained to a filter system to be re-circulated into the tank 10, or be dumped. Water entering the tank 10 from the inlet 42 is directed upward along the axis 16. This produces the upward flowing column of water 100. When the up flowing column of water 100 reaches the top of the tank, the water then flows as an outward flow 102 toward the screen 28 and the outlet system 22. A portion of this water flows through screen 28 into the outlet system 22 while the remaining portion of water flows as a downward flow shown by arrows 104 along the inside surface of the receptacle 12. This flow of water re-joins the upward flowing column 100 near the bottom 18. Thus in effect, the water entering the tank 10 from the inlet 42 generates a toroidal-like flow of water upwardly through a centre of the tank 10, outwardly toward the upper edge 24 downwardly along an inside surface of the tank 10 re-joining the upward flow 100 near the bottom 18.

Simultaneously, water is flowing into the tank 10 from the second inlet 50. This water flows initially tangentially to the inside surface of the receptacle 12 adjacent the inlet 50. This water then generates a circulating flow of water about the central axis 16 and the upward flowing column 100. The circulating flow of water generates a force on aquatic animals within the tank 10 which tends to keep the animals away from the inside surface 20. When the valve 56 is shut off or disconnected and the vent/or the valve 56 closed, the backflow of water through the inlets 42 or 50 is prevented by operation of the one-way valve 58. Additionally, aquatic animals are prevented from swimming any substantive distance into the inlet system 14 by the screens 70 and 72. These screens on the inlets also help to equalize water flow velocity and pressure (similar to the mesh in a mixer tap). If it is desired to drain the tank 10, the valve 56 is shut, and the valve 48 opened. Alternately water can be drained through the sockets 98.

A lower part of the frusto-conical portion 30 may be made of a transparent material to enable visual inspection of the inside of tank 10 near inlet 42. This part may extend for example form the inlet 42 to about one quarter of the way up the portion 32. The remainder of the receptacle 12 can be made of opaque material to prevent light entering the tank 10. Additionally an opaque lid (not shown) is provided that fits over the top of the tank 10 and has a depending circumferential wall that lies on an outside of the second gutter 86. A light tight seal or a light trap can be incorporated in the lid to prevent light entering the tank 10 from between the lid the outside of the second gutter 86.

Now that embodiments of the invention have been described in detail it will be apparent to those skilled in the art the numerous modifications and variations can be made without departing from the basic inventive concepts. For example the baffle block 45 could be replaced with a perforated horizontal plate if waste extraction through the inlet 42 is not required for the tank 10. Also the pipe 52 and inlet 50 may line on a line that is substantially horizontal, rather than being inclined. Modifications and variations in the aquaculture tank 10 that would be obvious to persons of ordinary skill in the art are deemed to be within the scope of the present invention the nature of. which is to be determined by the above description and the appended claims.